Accelerated bimolecular reactions in microdroplets studied by desorption electrospray ionization mass spectrometry

• DOI: 10.1039/c0sc00416b
• Publication Date: 2010-12-06T14:30:23Z
• Authors: Marion Girod; Encarnacion Moyano; Dahlia I. Campbell; R. Graham Cooks
• Keywords: Desorption electrospray ionization; Reaction rate

Functional group derivatization reactions occur in the course of microdroplet/surface collisions ambient ionization process desorption electrospray (DESI). The unique environment microdroplet causes rate enhancements as much several orders magnitude typical bimolecular that proceed through either cationic or anionic intermediates. evaporating charged differs from bulk: (i) pH solution moves towards extremes, (ii) concentrations reagents increase, (iii) relative surface area increases and (iv) collision frequencies increase. rates acid-catalyzed reactions, such reaction Girard T reagent with ketosteroids, increase decreasing positively-charged microdroplets compared to bulk rates. Similarly, increased negatively-charged contributes an base-catalyzed Michael over those recorded under conditions. amount product formed depends on time droplet size. Nanoelectrospray generates larger droplets than secondary DESI so it does not show significant formation analysis period can be used analyze products experiments. When (ca. 1 micron diameter) are generated by spraying a homogeneous both against inert (reactive DESI) when is sprayed solid bearing ketosteroid amounts generated. In case cinnamic acid alternative dehydrogenated Some parallels between phenomenon reported here acceleration seen sonochemistry noted. potential value mass spectrometry establishing conditions enhance also indicated. It possible these observations will assist selection involving use ordinary chemical especially strong steric hindrance.